欧几里德距离java实现

欧几里德距离是一个简单的相似度评价方法，返回0-1的值代表互相之间的相似度，1为完全相似

上代码：

package com.Social.cbra;


import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.logging.Logger;

/**
 *
 * @author larry
 *
 */
public class Similarity {
    static Logger logger = Logger.getLogger(Similarity.class.getName());
    Map<String, Double> rating_map = new HashMap<String, Double>();

    /**
     * @param args
     */
    public static void main(String[] args) {
        Similarity similarity1 = new Similarity();
        similarity1.rating_map.put("1", 1d);
        similarity1.rating_map.put("2", 1d);
        similarity1.rating_map.put("3", 1d);
        Similarity similarity2 = new Similarity();
        similarity2.rating_map.put("1", 1d);
        similarity2.rating_map.put("2", 1d);
        similarity2.rating_map.put("3", 1d);
        logger.info("" + similarity1.getsimilarity_bydim(similarity2));
        //System.out.println(rating_map.size());
    }

    public double getsimilarity_bydim(Similarity u) {
        double sim = 0d;
        double common_items = 0;

        Iterator<String> rating_map_iterator = rating_map.keySet().iterator();
        while(rating_map_iterator.hasNext()){
            String rating_map_iterator_key = rating_map_iterator.next();
            Iterator<String> u_rating_map_iterator = u.rating_map.keySet().iterator();
            while(u_rating_map_iterator.hasNext()){
                String u_rating_map_iterator_key = u_rating_map_iterator.next();
                if(rating_map_iterator_key.equals(u_rating_map_iterator_key)){
                    //相似度计数加一
                    //求差值的平方和
                    common_items++;
                    sim += Math.pow((u.rating_map.get(u_rating_map_iterator_key) - this.rating_map.get(rating_map_iterator_key)), 2);
                }
            }
        }

        //如果等于零则无相同条目，返回sim=0即可
        if(common_items > 0){
            //相似度的范围在0-1之间//tanh取值范围-1到1
            //0表示完全不相似
            //1表示完全相似
            //求平均后开跟
            //乘上相同的数量占最大可能相同的数量的比重
            sim = Math.sqrt(sim/common_items);
            sim = 1.0d - Math.tanh(sim);
            int max_common_items = Math.min(rating_map.size(), u.rating_map.size());
            sim = sim * (common_items/max_common_items);
        }
        return sim;
    }

}

转自：http://www.itivy.com/java/archive/2012/3/13/634672518556702882.html